St. Clairsville, Ohio-based Murray Energy filed a brief with the U.S. Circuit Court of Appeals for the District of Columbia on Monday, challenging the EPA's supplemental finding published earlier in the day.

The U.S. Supreme Court ruled last year that the EPA should have considered the costs and benefits before imposing limits on mercury and other air pollutants from coal- and oil-fired power plants. The high court let the rule stay in effect and sent it back to the federal appeals court in Washington to decide how a cost-benefits analysis should be conducted.

The EPA heard public comments and said it determined after considering costs that the regulation of emissions is appropriate and necessary, and that those power plants were properly included for regulation under the Clean Air Act.

Twenty states had urged the Supreme Court to block the rule while the government decided how to account for its costs. In December a three-judge panel unanimously rejected the states' request to postpone the rule.

The states, led by Michigan, argued that leaving the rule in place had already imposed billions of dollars of compliance costs on utility companies. They said it was unfair to keep it intact even after the Supreme Court said the EPA ignored the cost to power plants.

A coalition of environmental groups and states supporting the rule urged the high court to keep it in place.